Easy processing and flexibility of polymer electrolytes make them very promising in developing all-solid-state lithium batteries. However, their low room-temperature conductivity and poor mechanical and thermal properties still hinder their applications. Here, we use LiLaZrTaO (LLZTO) ceramics to trigger structural modification of poly(vinylidene fluoride) (PVDF) polymer electrolyte. By combining experiments and first-principle calculations, we find that La atom of LLZTO could complex with the N atom and C═O group of solvent molecules such as N,N-dimethylformamide along with electrons enriching at the N atom, which behaves like a Lewis base and induces the chemical dehydrofluorination of the PVDF skeleton. Partially modified PVDF chains activate the interactions between the PVDF matrix, lithium salt, and LLZTO fillers, hence leading to significantly improved performance of the flexible electrolyte membrane (e.g., a high ionic conductivity of about 5 × 10 S cm at 25 °C, high mechanical strength, and good thermal stability). For further illustration, a solid-state lithium battery of LiCoO|PVDF-based membrane|Li is fabricated and delivers satisfactory rate capability and cycling stability at room temperature. Our study indicates that the LLZTO modifying PVDF membrane is a promising electrolyte used for all-solid-state lithium batteries.
The development of
anhydrous proton-conducting materials is critical
for the fabrication of high-temperature (>100 °C) polymer
electrolyte
membrane fuel cells (HT-PEMFCs) and remains a significant challenge.
Covalent organic frameworks (COFs) are an emerging class of porous
crystalline materials with tailor-made nanochannels and hold great
potential for ion and molecule transport, but their poor chemical
stability poses great challenges in this respect. In this contribution,
we present a bottom-up self-assembly strategy to construct perfluoroalkyl-functionalized
hydrazone-linked 2D COFs and systematically investigate the effect
of different lengths of fluorine chains on their acid stability and
proton conductivity. Compared with their nonfluorous parent COFs,
fluorinated COFs possess structural ultrastability toward strong acids
as a result of enhanced hydrophobicity (water contact angle of 144°).
Furthermore, the superhydrophobic 1D nanochannels can serve as robust
hosts to accommodate large amounts of phosphonic acid for fast and
long-term proton conduction under anhydrous conditions and a wide
temperature range. The anhydrous proton conductivity of fluorinated
COFs is 4.2 × 10–2 S cm–1 at 140 °C after H3PO4 doping, which is
4 orders of magnitude higher than their nonfluorous counterparts and
among the highest values of doped porous organic frameworks so far.
Solid-state NMR studies revealed that H3PO4 forms
hydrogen-boding networks with the frameworks and perfluoroalkyl chains
of COFs, and most of the H3PO4 molecules are
highly dynamic and mobile while the frameworks are rigid, which affords
rapid proton transport. This work paves the way for the realization
of the target properties of COFs through predesign and functionalization
of the pore surface and highlights the great potential of COF nanochannels
as a rigid platform for fast ion transportation.
All-solid-state bulk-type lithium ion batteries (LIBs) are considered ultimate solutions to the safety issues associated with conventional LIBs using flammable liquid electrolyte. The development of bulk-type all-solid-state LIBs has been hindered by the low loading of active cathode materials, hence low specific surface capacity, and by the high interface resistance, which results in low rate and cyclic performance. In this contribution, we propose and demonstrate a synergistic all-composite approach to fabricating flexible all-solid-state LIBs. PEO-based composite cathode layers (filled with LiFePO particles) of ∼300 μm in thickness and composite electrolyte layers (filled with Al-LLZTO particles) are stacked layer-by-layer with lithium foils as negative layer and hot-pressed into a monolithic all-solid-state LIB. The flexible LIB delivers a high specific discharge capacity of 155 mAh/g, which corresponds to an ultrahigh surface capacity of 10.8 mAh/cm, exhibits excellent capacity retention up to at least 10 cycles and could work properly under harsh operating conditions such as bending or being sectioned into pieces. The all-composite approach is favorable for improving both mesoscopic and microscopic interfaces inside the all-solid-state LIB and may provide a new toolbox for design and fabrication of all-solid-state LIBs.
Figure 3. a) The mechanism of the movement of Li + along the PEO chain. Reproduced with permission. [42] Copyright 2006, Elsevier. b) The phaseseparation model of adding succinonitrile into a PEO/LiTFSI electrolyte system. c) TEM image of PEO-succinonitrile/LiTFSI electrolyte. d) Comparison of the ionic conductivity of PEO-succinonitrile/LiTFSI and PEO/LiTFSI electrolytes. e) Linear elastic tensile modulus of PEO-succinonitrile/LiTFSI with varying LiTFSI content. Reproduced with permission. [45]
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.